1. Field of the Invention
The present invention relates to a fuel injector for use in, for example, a gas turbine engine and, more particularly, to the fuel injector equipped with a complex fuel injector comprised of a plurality of fuel nozzles.
2. Description of Related Art
In recent years, in consideration of the environment, there is a need for a reduction of emissions such as NOx (nitrogen oxide) emitted from gas turbine engines. A fuel injector of the conventional aircraft gas turbine combustor is of a diffusive combustion type, and since in the diffusion combustion, the burning reaction takes place based on the stoichiometric mixture ratio, the flame temperature tends to increase. Considering that the emission of NOx is known to exponentially increase with the increase of the flame temperature, lowering of the flame temperature appears to effectively suppress the emission of NOx. However, in the current situation of the propensity for high temperature and high pressure in the gas turbine, further suppression of the emission of NOx with the conventional diffusive combustion method is limited.
In order to lower the flame temperature, a fuel injector of a lean premixed combustion method is considered effective. The lean premixed combustion method is known to be a method of burning an air-fuel mixture in which the ratio of fuel relative to air is lowered, and the lean combustion according to this method contributes to a considerable reduction of the flame temperature as compared with that afforded by the conventional diffusive combustion method. On the other hand, however, the lean premixed combustion method tends to result in an instable and incomplete combustion of the air-fuel mixture because of the relatively low flame temperature. In view of this, a concentric fuel injector has been used to realize a low NOx emission, in which while a pilot fuel injector is located on an inner side and a main injector is located coaxially with, and outer side of the pilot fuel injector. In the concentric fuel injector, the diffusive combustion method with the pilot fuel injector is used to maintain a stable combustion at a low power operation, while the lean premixed combustion method with the main fuel injector is used in addition to the diffusive combustion with the pilot fuel injector at a high power operation.
With the concentric fuel injector referred to above, fuel is injected into a stream of air to form a premixed air-fuel mixture within a premix flow path of the main fuel injector so that the above discussed lean combustion may be realized by burning the premixed air-fuel mixture within a combustion chamber. As the structure necessary for the fuel to be injected into the stream of air, a structure in which a fuel injection unit is located in a wall surface of the air flow path and the fuel is injected towards an outer diameter side or an inner diameter side (such as addressed in the patent documents 1 and 2 listed below), a structure in which fuel injection units are located in between two air flow paths located on an inner diameter side and an outer diameter side, respectively, and fuel is injected into both of those air flow paths (such as addressed in the patent document 3 listed below), and a structure in which of the two air flow paths located on an inner diameter side and an outer diameter side, respectively, a fuel injection unit is located outside the air flow path on the outer diameter side so that the fuel may be injected into the air flow path on the outer diameter side so as to flow towards the inner diameter side (such as addressed in the patent document 4 listed below), have been suggested.